Radiation detector tube



Filed Nov. 17, 1953 United States Patent O RADIATION DETECTOR TUBENicholas Anton, Brooklyn, N. Y.

Application November 17, 1953, Serial No. 392,604

8 Claims. (Cl. 313-93) The present invention relates to the artincluding radiation detectors and is more particularly concerned withimprovements in the structure of proportional and Geiger counter tubes.

Geiger and proportional counter tubes have been found to be useful inX-ray spectroscopy, particularly for soft X-rays such as obtained fromcopper. In such tubes, the use of krypton gas has been found to beadvantageous, but such use has been inhibited because of the formerdifficulty of reducing spurious counts.

According to the present invention, simple and effective means have beendiscovered which eliminate spurious counts in such tubes, andaccordingly it is a primary object of the present invention to providean improved radiation detector tube structure in which spurious countsare eliminated or minimized.

Other advantages and objects of the present invention will become morefully apparent from consideration of the following description taken inconjunction with the appended drawing, which in its single figure showsa longitudinal cross sectional view of an axially symmetrical detectortube according to the present invention.

Referring to the single figure of the drawing, the tube of the presentinvention comprises a cylindrical cathode electrode 11 forming also amajor portion of the envelope of the device. Sealed to the cathode 11 atone end 32 thereof is an insulator 12, such as of ceramic material orthe like, to which in turn at 33 is sealed the anode support 13 formedof conductive material. The anode 14 is supported in cantilever fashionfrom the anode support 13 and is formed by a stiff wire such as .025"diameter stainless steel wire. The anode support 13 has a bore 16extending transversely thereof and a bore 17 extending axially thereof.An exhaust tubulation communicates with and is sealed with the bore 17of anode support 13. The remainder of the enclosure of the device isprovided by a radiation-permeable window 19 formed of plastic, mica orthe like, and sealed at 31 to cathode 11. The material of this window isnot critical, provided that it has a low weight per unit area and may,for example, be 1.4 milligrams per square centimeter in area density.

In usual fashion the envelope formed of window 19, cathode 11, insulator12 and anode support 13 is evacuated through the tubulation 18 and isthen filled with a suitable gas and a quenching agent. The preferred gaslling is krypton at pressures ranging from 300 -to 600 millimeters ofmercury, and the quenching agent used is a halogen, such as bromine,chlorine or a mixture of both. An anode terminal 21 is secured to theanode support 13 as by threading and/or soldering to form one terminalfor the device, the other terminal being formed by the conductivecathode casing. A glass or other insulating bead 22 is formed at the tipof the anode wire 14 to prevent accidental contact with cathode 11 andto avoid corona discharge at the tip of the anode wire.

A tube such as that just described is subject to the spurious countdisadvantage indicated above. According to the present invention, thisspurious count formation is eliminated by introducing a cathodeinsulator sleeve 23 Within the cathode 11 at the window end thereof andextending for a short distance inwardly, such as of the ICC order of 1Ato 1/2 inch out of a total length of cathode of approximately 5 inches.This insulator is short in an axial direction to allow the electricfield to extend close to the mica window 19 to permit counting of theelectrons generated by 'the impinging X-ray beams as soon as they enterthe tube.

While the manner in which this sleeve 23 operates to eliminate spuriouscounts is not fully clear, it is believed 4that it does so byeliminating the field concentration due to termination of anode Wire 14in insulating bead 22.

it will be understood that in some cases it may be advantageous to omitthe glass bead 22 entirely or to form a conductive bulbous tip at theend of the anode Wire 14.

it is to be understood that the above description is to be taken asillustrative only since the present invention may assume apparentlywidely different forms without departing from the spirit thereof, thescope of the invention being defined solely by the appended claims.

What is claimed is:

l. A radiation detector comprising a cylindrical cathode electrode, aradiation-permeable window sealed across one end of said cathode, aninsulator sealed at the other end of said cathode, an anode supportmounted on and sealed to said insulator, an anode wire mounted coaxiallywithin said cathode and supported only at one end by said insulator andterminating at the other end in a tip adjacent said window, said tipbeing within said cathode, an exhaust tubulation sealed to said anodesupport and completing the envelope of said tube, and an insulatingsleeve lining the interior of said cathode adjacent said window andsurrounding said anode wire tip for reducing spurious counts.

2. A detector tube as in claim l, wherein said anode wire tip is formedby an insulating bead sealed to the end of said anode wire.

3. A detector tube as in claim 2, wherein said anode wire tip is formedby a glass bead sealed on the end of said anode wire.

4. A detector tube as in claim 1, wherein said envelope contains kryptongas at a pressure between 300 and 600 millimeters of mercury.

5. A radiation detector tube as in claim 4, wherein said envelope alsocontains a halogen quenching gas.

6. A detector as in claim l, wherein said window is permeable to softradiation and has an area weight of the order of 1.4 milligrams persquare centimeter.

7. A radiation detector tube comprising a gas-tight envelope, saidenvelope comprising a cylindrical cathode and an'insulatingradiation-permeable window sealed at one end of said cylindricalcathode, a krypton gas filling within said envelope, an anode mountedcoaxially within said cathode and insulated and spaced therefrom, saidanode being supported only at the end thereof opposite said window andterminating adjacent said window in-a tip, said tip being within saidcathode, and an insulating sleeve lining said cathode adjacent saidwindow and surrounding said anode tip whereby spurious counts areinhibited.

8. A radiation detector tube comprising a gas-tight envelope comprisinga hollow axially symmetrical conductive cathode having aradiation-permeable window at one end, an anode mounted coaxially withinsaid cathode and having an end adjacent said window and Within saidcathode, and an insulating sleeve lining the interior of said cathodeadjacent said window and surrounding said anode end, whereby spuriouscounts are inhibited.

References Cited inthe file of this patent UNITED STATES PATENTS2,479,201 Bleeksma Aug. 16, 1949 2,542,440 Victoreen et al Feb. 20, 19512,612,615 Fehr et al. Sept. 30, 1952

